1. Field of the Invention
The present invention relates to a developing device structure employed for an electrophotographic recording apparatus such as a printer, a copier, etc.
2. Description of the Related Art
A developing device of this type is disclosed in the EPC Publication No. 0435259A3 filed by the present applicant.
In this developing device, a toner is supplied from a toner cartridge to a developing portion to be collected in a toner hopper portion, and is stirred by a stirring means provided in the toner hopper portion. Thereafter the toner is supplied to a photoconductor drum via a supply roller and developing roller.
In some electrophotographic recording apparatus, an indicator for positioning the printing paper is set at the central portion of the printing paper in the width direction thereof. Such an electrophotographic recording apparatus has typically a stirring means for the developing device as illustrated in FIG. 20.
A toner hopper stirring means 80 comprises a shaft 19 and helical members 81a and 81b respectively formed of springs. The helical members 81a and 81b have the same coil diameters and the same winding pitches. The helical members 81a and 81b are wound around the shaft in the directions opposite to each other. When the shaft 19 of the toner hopper stirring means 80 is turned in the direction of the arrow C, the toner positioned at both ends of the shaft 19 is stirred and moved toward the central portion of the shaft 19. If the feeding standard of the electrophotographic recording apparatus is set at the central portion of the printing papers, the printing frequency is increased at the central portion of the photoconductor drum when printing is performed on printing papers having different sizes, so that much toner is consumed at the central portion of the toner hopper portion in the developing device but is supplemented with the toner which is moved toward the central portion of the toner hopper portion by the toner hopper stirring means 80.
However, in the conventional developing apparatus, the toner collected in the toner hopper portion is always conveyed by the toner hopper stirring means toward the central portion of the toner hopper portion at a constant speed and supplied to the supply roller of the developing portion.
Accordingly, there is no problem when the amount of toner collected in the toner hopper portion is enough to sufficiently cover the toner hopper portion but there arises the problem that the toner is locally positioned at the central portion of the toner hopper portion and is reduced at both ends of the toner is hopper portion when the amount of toner reduced to such an extent that it does not sufficiently cover the toner hopper stirring portion. If printing is performed in the latter case, there is a problem that a printing irregularity occurs on the printing paper, which deteriorates the printing quality. Especially, if printing few characters on a printing paper continues, the printing quality is remarkably deteriorated.